Portable ultrasonic imaging probe including transducer array

ABSTRACT

The invention provides a portable ultrasonic imaging probe directly connectable to an off-the-shelf laptop computer. The probe produces raw digitized data comprising envelope detected ultrasound echo data from an array of ultrasound transducers, and transmits the data to the host computer thereby enabling the host computer to form real-time ultrasonic images of human tissue without the need for any additional electronics. In particular embodiments, the probe includes a plurality of transmit switches configured to connect a transmitting group of the ultrasound transducers to a pulser; a plurality of receive switches configured to connect a receiving group of the ultrasound transducers to analog summing, amplification and signal processing circuitry; and a transmit/receive controller which selects which of said ultrasound transducers are in the transmitting group and which of said ultrasound transducers are in the receiving group. The ultrasound transducers may be conventional or micromachined ultrasound transducers.

PRIORITY CLAIM

This application claims the benefit of priority to U.S. Provisional Patent Application No. 61/676,193 filed Jul. 26, 2012 entitled “PORTABLE ULTRASOUND IMAGING PROBE INCLUDING MEMS BASED TRANSDUCER ARRAY” which application is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to portable ultrasonic imaging probes, and more specifically, to such probes including a transducer array, wherein such probes can be directly connected to a host computer, such as an off-the-shelf laptop computer, or the like.

BACKGROUND

Typically, ultrasound imaging systems include a hand-held probe that is connected by a cable to a relatively large and expensive piece of hardware that is dedicated to performing ultrasound signal processing and displaying ultrasound images. Such systems, because of their high cost, are typically only available in hospitals or in the offices of specialists, such as radiologists. Recently, there has been an interest in developing more portable ultrasound imaging systems that can be used with personal computers. Preferably, such a portable ultrasound probe can be used with an off-the-shelf host computer, such as a personal computer, and is inexpensive enough to provide ultrasound imaging capabilities to general practitioners and health clinics having limited financial resources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a high level diagram showing elements of the present invention.

FIG. 1B illustrates an ultrasonic imaging probe according to an embodiment of the present invention originally described with reference to FIG. 1A.

FIG. 2A is a block diagram that shows additional details of an ultrasonic imaging probe according to an embodiment of the present invention.

FIG. 2B illustrates some further details of some of the blocks introduced in FIG. 2A, according to an embodiment of the present invention.

FIG. 2C illustrates a perspective view of a probe head assembly, according to an embodiment of the present invention.

FIG. 2D illustrates how odd and even rows of transducers can be staggered relative to one another according to an embodiment of the present invention.

FIG. 2E illustrates an alternative array of ultrasound transducers according to an embodiment of the present invention.

FIG. 2F is a block diagram that shows details of an alternative ultrasonic imaging probe according to an embodiment of the present invention.

FIG. 3A shows how sets of micromachined ultrasound transducers can be used to form a moving quasi-annular array transducer according to an embodiment of the present invention.

FIG. 3B is a blown-up view of two of the vectors shown in FIG. 3A.

FIGS. 3C-3F show how sets of ultrasound transducers can be used to form a moving square array transducer according to an embodiment of the present invention.

FIGS. 4A-4D illustrate a transmit sequence, according to an embodiment of the present invention.

FIGS. 5A-5D illustrate a receive sequence, according to an embodiment of the present invention.

FIGS. 6A-6D illustrate a receive sequence, according to an embodiment of the present invention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments. It is to be understood that other embodiments may be utilized and that mechanical and electrical changes may be made. The following detailed description is, therefore, not to be taken in a limiting sense. In the description that follows, like numerals or reference designators will be used to refer to like parts or elements throughout. In addition, the first digit of a reference number identifies the drawing in which the reference number first appears.

FIG. 1A shows an ultrasonic imaging probe 102, according to an embodiment of the present invention, which is connected by a passive interface cable 106 to a host computer 112. Ultrasonic imaging probe 102 includes an array of ultrasound transducers for transmitting and receiving ultrasound pulses as will be described below. The host computer 112 can be a desktop personal computer (PC), a laptop PC, a pocket PC, a tablet PC, a mobile phone capable or running software programs (often referred to as a “smart phone”), a personal digital assistant, or the like. The passive interface cable 106, which includes connectors and passive wires, can be a Universal Serial Bus (USB) cable (e.g., a USB 2.0 cable), a FireWire (also known as IEEE 1394) cable, or the like. Preferably the probe 102 is not connected to any other device or power supply. Thus, in a preferred embodiment the probe 102 receives all its necessary power from the host computer 112 via the passive interface cable 106. In alternative embodiments, probe 102 can include a battery and a wireless transceiver, in which case the probe can wireless communicate with the host computer, and the probe can generate all its necessary power from the battery.

As will be described in more detail below, in accordance with embodiments of the present invention, the probe 102 enables the host computer 112, via software running on the host computer 112, to form real-time ultrasonic images of a target 100 (e.g., human tissue or other materials) without the need for any additional internal or external electronics, power supply, or support devices. In certain embodiments, the probe 102 produces raw digitized data that is envelope detected ultrasound echo data from an array of ultrasound transducers in the probe 102, and transmits such raw data to the host computer 112. The raw digitized data can optionally also be logarithmically compressed, depending upon implementation.

In an embodiment, when the host computer 112 receives raw data via the passive interface cable 106 from the probe 102, the host computer 112 performs time gain compensation (TGC), gray-scale mapping, and scan conversion of the raw data using software that runs on the host computer 112, and displays the resultant video images. The probe does not include any moving mechanical parts, thereby reducing the complexity and cost of the probe 102 and increasing its reliability. The term “raw data”, as used herein, refers to ultrasound imaging data that has not yet been time gain compensated, gray-scale mapped and scan converted. As described below, such raw data is included in the digital signal that is transferred from the probe 102 to the host computer 112.

As shown in FIG. 1A, the host computer 112 will likely include a communications port 108, a communications chip-set 122, a central processing unit (CPU) 124, memory 126, a display 128, and an input device 130, such as a keyboard, mouse, touch screen, track ball, or the like. Additionally, the host computer 112 runs software that enables the host to control specific aspects of the probe 102. Such software also enables the host computer 112 to perform time gain compensation (also known as time gain correction), gray-scale mapping, and scan conversion of the raw data received from the probe 112 over the passive interface cable 106. The host computer 112 can then display the resulting ultrasound video on the display 128, as well as store such video in its memory 126, or another data storage device (not shown).

The article “A New Time-Gain Correction Method for Standard B-Mode Ultrasound Imaging”, by William D. Richard, IEEE Transactions of Medical Imaging, Vol. 8, No. 3, pp. 283-285, September 1989, which is incorporated herein by reference, describes an exemplary time gain correction technique that can be performed by the host computer 112. The article “Real-Time Ultrasonic Scan Conversation via Linear Interpolation of Oversampled Vectors,” Ultrasonic Imaging, Vol. 16, pp. 109-123, April 1994, which is incorporated herein by reference, describes an exemplary scan conversion technique that can be performed by the host computer 112. These are just exemplary details of the host computer 112, which are not meant to be limiting.

The passive interface cable 106 includes at least one data line over which data is carried, and at least one power line to provide power to a peripheral device, which in this case is the ultrasonic imaging probe 102. For example, where the passive interface cable 106 is a USB 2.0 cable, one wire of the cable provides about 5V at about ½ Amp. In alternative embodiments, the passive interface cable 106 is a Firewire cable, which also includes a power wire. Other types of passive interface cable can be used if desired. However, as mentioned above, it is preferred that the passive interface cable 106 is a standard off-the-shelf cable that can interface with an off-the-shelf interface IC. The term passive as used herein refers to a cable that does not regenerate signals or process them in any way. In an alternative embodiment, the probe 102 and the host computer 112 communicate wirelessly, and the probe 102 includes a battery that is used to power the components within the probe.

FIG. 1B illustrates an example where the host computer 112 is a laptop. FIG. 1B also shows an exemplary ergonomic design of a housing 103 for the ultrasonic imaging probe 102 of the present invention. Other ergonomic designs are of course possible, and within the scope of the present invention. Also, as explained above, other types of host computer 112 can also be used. FIG. 1B also shows that the ultrasonic imaging probe 102 includes a probe head assembly 105.

In accordance with certain embodiments, the data samples produced by the ultrasound imaging probe 102 of the present invention are transmitted by the probe 102 across the interface cable 106 to the host computer 112. In a specific embodiment, this is accomplished when the host computer 112 reads the data temporarily stored in the buffers of the interface IC 204. The host computer 112 runs software that enables the host to perform time gain compensation (TGC), gray-scale mapping, and scan conversion of the data received from the probe 102. The host computer generates and displays the resultant ultrasound video images. Advantageously, the host computer 112 does not need to perform electronic beamforming or other equivalent image processing, thereby simplifying the software that the host computer 112 runs.

The host computer 112 can use the digital data received from the ultrasound device 102 to provide any available type of ultrasound imaging mode can be used by the host computer 112 to display the ultrasound images, including, but not limited to A-mode, B-mode, M-mode, etc. For example, in B-mode, the host computer 112 performs know scan conversion such that the brightness of a pixel is based on the intensity of the echo return.

A benefit of specific embodiments of the present invention is that only digital signals are transmitted from the probe 102 to the host computer 112, thereby providing for better signal-to-noise ratio than if analog signals were transmitted from the probe 102 to the host computer 112, or to some intermediate apparatus between the host computer and the probe. Another benefit of specific embodiments of the present invention is that the probe 102 can be used with a standard off-the-shelf passive interface cable.

A further benefit of specific embodiments of the present invention is that the probe 102 does not perform any time gain compensation, gray-scale mapping and scan conversion, thereby significantly decreasing the complexity, power requirements and cost of the probe 102. Conventionally, functions such as scan conversion, time gain correction (also known as time gain compensation) and gray-scale mapping are performed by a machine that is dedicated to obtaining ultrasound images, or by an intermediate device that is located between the probe and host computer. In contrast, in embodiments of the present invention, software running on the host computer 112 is used to perform these functions, thereby reducing the complexity and cost of the portable ultrasonic imaging probe 102.

FIG. 2A is a block diagram that shows additional details of an ultrasonic imaging probe according to an embodiment of the present invention. Additional details of the ultrasonic imaging probe 102, according to specific embodiments of the present invention, shall now be described with reference FIG. 2A. As shown in FIG. 2A, in accordance with an embodiment of the present invention, the probe 102 includes a peripheral connector 104 and an interface IC 204 that enables the probe 102 to interface with the host computer 112 via the interface cable 106. The connector 104 and the interface IC 204 are preferably off-the-shelf devices, but can be custom devices.

In accordance with an embodiment illustrated in FIG. 2A, specific certain components (shown within a large dash-lined rectangle) are located within the probe head assembly 105, with the remaining components being within the housing 103 of the ultrasonic imaging probe 102. An interface cable 209 connects the components within the housing 103 to the components within the probe head assembly 105.

The probe 102 is also shown as including a digital control and processing block 206, an analog to digital converter (ADC) 208 and a high voltage power supply (HVPS) 250. The HVPS 250 provides power to a high voltage (HV) pulser 224. Additionally, the probe 102 is shown as including a micromachined ultrasound transducer (MUT) array 220, which includes individually controllable MUT elements 221, which are discussed in additional detail below. A transmit and receive (Tx/Rx) controller 240 accesses vector configuration and timing data stored within a memory 230 in order to controls transmit (Tx) switches 222 and receive (Rx) switches 216, to thereby control the operation of the MUT elements 221 of the MUT array 220, as described in additional detail below. In certain embodiments, such vector configuration and timing data is stored within a look-up table (LUT) within the memory 230.

The probe 102 also includes analog summing, amplification and processing circuitry 215. In accordance with an embodiment, the analog summing, amplification and processing circuitry 215 includes summing resistors 214 and a summing amplifier 212, which are discussed in more detail with reference to FIG. 2B, and an analog signal processing block 210. The analog signal processing block 210 can include, e.g., a pre-amplifier, a filter (e.g., a low pass or bandpass filter) and an envelope detector, and optionally a logarithmic amplifier. Such a pre-amplifier can be, e.g., a very low noise amplifier that provides about 20 dB of gain. The filter can filter out frequencies that are not of interest. The summing resistors 214 and the summing amplifier 212 combine numerous echo signals (received using numerous MUT elements) into a single echo signal. In accordance with an embodiment, this single echo signal is pre-amplified, filtered (e.g., low pass filtered) and envelope detected to produce a radio frequency (RF) signal. Logarithmic compression can be performed within the analog signal processing block 210, or within the digital control and processing block 210, or alternatively, within the host computer 112.

The RF signal output by the analog signal processing block 210 is digitized by the ADC 208. The ADC 208 samples the RF signal (e.g., at 30 or 48 MHz), to thereby digitize the signal, and provides the digitized signal to the digital control and processing block 210. The digital control and processing block 206 could be implemented, e.g., using a complex programmable logic device (CPLD), a field-programmable gate array (FPGA), an application specific integrated circuit (ASIC) or some other circuitry. The digital control and processing clock 206 control functions and timing of the hardware in the probe, and depending upon implementation, can also perform digital signal processing of the digital signal output by the ADC 208. For example, the digital control and processing block 206 can perform logarithmic compression, as was mentioned above. The digital control and processing clock 206 also controls the Tx/Rx controller 240.

The Tx/Rx controller 240, which can be implemented using an FPGA, an ASIC or some other circuitry, controls the Tx switches 222 so that a selected set of the MUTs transmit ultrasonic pulses generated by a high voltage (HV) pulser 224. The host computer 112, through the passive interface cable 106, and the interface IC 204 can control the amplitude, frequency and duration of the pulses output by the HV pulser 224. For example, the host computer 112 can write vector configuration and timing data to the memory 230. Additionally, the host computer 112 can send instructions to the probe 102 that cause the probe 102 to select, from the memory 230, specific transmit and receive vector control and timing data used to control transmission and reception of ultrasonic pulses.

The HV pulser 224 is powered by the HVPS 250, which generates the high voltage potential(s) required by the HV pulser 224 from a lower voltage (e.g., 5V) received via the passive interface cable 106. Depending upon implementation, the HV pulser 224 can produce unipolar pulses, or bipolar pulses. Unipolar pulses can be, e.g., high voltage pulses that are as large as 100V. Where the HV pulser 224 produces bipolar pulses, the HV pulser 224 may produce, e.g., both positive and negative high voltage pulses that can be as large as +/−100V. In such embodiments, the HVPS 250 can provide up to +/−100V supply rails to the HV pulser 224. Exemplary details of an HVPS, which can be used to implement the HVPS 250, are shown in and described with reference to FIG. 4 of U.S. Patent Publication No. 2007/0239019, which U.S. Patent Publication is incorporated herein by reference in its entirety. Alternative high voltage power supplies known in the art may also used as HVPS 250.

The probe 102 can also include a linear regulator IC (now shown) with integrated power switches and low quiescent current requirements designed for USB applications. For example, such a linear regular IC can produce a 3.3V digital supply and a 3.3V analog voltage supply, which are used to provide power to the various circuits/blocks within the probe 102. For example, a 3.3V digital supply can power the interface IC 204 and the digital control and processing block 206; and a 3.3V analog supply can power the summing amplifier 212 and the analog signal processing circuitry 210. An exemplary IC that can be used for the linear regulator IC is the TPS2148 3.3-V LDO and Dual Switch for USB Peripheral Power Management IC, available from Texas Instruments of Dallas, Tx.

Preferably, the probe 102 is configured as a single channel architecture, which means that only a single ADC 208 is required, and only a single data signal is transmitted from the probe 102 to the host 112 at any given time. However, in alternative embodiments, a multiple channel architecture that includes multiple ADCs can be implemented. Unless stated otherwise, the embodiments described herein include a single channel architecture. Another benefit of specific embodiments of the present invention is that the MUT array 220 is in close proximity to (i.e., within the same housing as) the analog summing, amplifying and processing circuitry 215 and the ADC 208 (see FIG. 2A). This provides for good signal-to-noise (S/N) ratio, as compared to systems where the analog signals output by the transducers must travel across a relatively long distance before they are amplified and/or digitized.

As mentioned above, the portable ultrasound imaging probe 102 includes an array of ultrasound transducers, which includes numerous transducers. In a preferred embodiment, the portable ultrasound imaging probe 102 includes a micromachined ultrasound transducer (MUT) array 220, which includes numerous MUTs 221, each of which can be referred to as an MUT element (or simply as an MUT). Each MUT element can include a single MUT cell, or multiple MUT cells hardwired together. Such a MUT array 220, which can also be referred to as an array of MUTs, is an example of a MEMS based transducer, since the MUTs are examples of micro-electro-mechanical systems (MEMS). A MUT is one example of an ultrasound transducer. However, the principles of the present invention are also applicable to arrays of ultrasound transducers and ultrasound transducers other than MUTs. Thus, although the following description refers to MUTs, alternative ultrasound transducers and transducer arrays can be used in place of the MUTs and MUT arrays described below.

Each MUT cell can be a capacitive MUT (cMUT) cell or a piezoelectric MUT (pMUT) cell, but is not limited thereto. Such cells typically include a membrane (often referred to as a diaphragm) and two or more electrodes. For transmission, the electrodes and membrane are used to modulate a capacitive charge that vibrates the membrane and thereby transmits a sound wave. For reception, the electrodes and membrane are used to convert the sound vibration of a received ultrasound signal into a modulated capacitance. More specifically, when an AC signal is applied across the electrodes, the MUT generates ultrasonic waves in the medium of interest to thereby function as a transmitter. When ultrasonic waves are applied to the membrane of a MUT, the MUT generates an alternating signal as the capacitance of the MUT is varied to thereby function as a receiver of ultrasonic waves.

Each MUT element can simply be referred to as an MUT, and a plurality of MUT elements can simply be referred to as MUTs. Preferably, the MUT array 220 is encased in material that has the proper acoustic impedance to be matched with acoustic impedance of human tissue.

Advantageously, MUTs can be made using semiconductor fabrication processes, such as microfabrication processes generally referred to as “micromachining” Micromachining is the formation of microscopic structures using patterning, deposition and/or etching. Patterning generally includes lithography, which can be performed using projection-aligners or wafer-steppers, but is not limited thereto. Deposition can be physical vapor deposition (PVD), chemical vapor deposition (CVD), low-pressure chemical vapor deposition (LPCVD), or plasma chemical vapor deposition (PECVD), but is not limited thereto. Etching can include wet-chemical etching, plasma-etching, ion-milling, sputter-etching or laser-etching, but is not limited thereto.

Micromachining is typically performed on substrates or wafers made of silicon, glass, sapphire or ceramic. Such substrates or wafers are generally very flat and smooth and have lateral dimensions in inches. They are usually processed as groups in cassettes as they travel from process tool to process tool. Each substrate can advantageously (but not necessarily) incorporate numerous copies of a product. Micromachining can include the use of conventional or known micromachinable materials including silicon, sapphire, glass materials of all types, polymers (such as polyimide), polysilicon, silicon nitride, silicon oxynitride, thin film metals such as aluminum alloys, copper alloys and tungsten, spin-on-glasses (SOGs), implantable or diffused dopants and grown films such as silicon oxides and nitrides, but is not limited thereto.

In accordance with an embodiment, the MUT array 220 includes M rows×N columns of transducer elements, with the MUTs 221 being illustrated as small circles in FIG. 2A. For example, if M=20 and N=100, then the MUT array would include 2000 MUTs. In accordance with an embodiment, half of the MUTs 221 can be selectively used for transmitting ultrasonic pulses, and the other half of the MUTs 221 can be selectively used for receiving “echo pulses”. Continuing with the example where the MUT array 220 includes 2000 MUTs, then 1000 of the MUTs 221 can be can be selectively used for transmitting ultrasonic pulses, and 1000 of the MUTs 221 can be selectively used for receiving “echo pulses”. More generally, P1 percent of the MUTs can be selectively used for transmitting ultrasonic pulses, and P2 percent (where P2=100%−P1) of the MUTs can be selectively used for receiving “echo pulses”. Unless specified otherwise, it will be assumed that P1=P2=50%, such that half of the MUTs can be selectively used for transmitting ultrasonic pulses, and half of the MUTs can be selectively used for receiving “echo pulses”. For illustrative purposes, the MUTs that can be used for transmitting ultrasonic pulses, which can be referred to as Tx MUTs, are illustrated in FIG. 2A as small filled circles 223; and the MUTs that can be used for receiving ultrasonic pulses, which can be referred to as Rx MUTs, are illustrated in FIG. 2A as small unfilled circles 225.

Each of the MUTs 221 can have a circumferential shape that is circular, as shown. Each MUT 221 can be, e.g., about 50 micrometers in diameter, but is not limited thereto. The distance from the edge of one MUT 221 to its closest adjacent MUT 221 can be, e.g., about 70 micrometers, but is not limited thereto. Alternatively, each of the MUTs can have another circumferential shape, including, but not limited to, square or hexagonal. In accordance with certain embodiments, the Tx MUTs 223 and the Rx MUTs 225 are structurally the same. In such embodiments, the only difference between a Tx MUT 223 and an Rx MUT 225 is how the MUT is connected to other circuitry and used. In other embodiments, the Tx MUTs 223 can be structurally different from the Rx MUTs 225. In alternative embodiments, each of MUTs 221 may be replaced with conventional ultrasound transducers which may be square or circular in shape (see, e.g. FIGS. 2E and 2F).

All of the rows and columns can be inline with one another, as shown in FIG. 2A. Alternatively, odd rows can be staggered relative even rows, as shown in FIG. 2D. It is also possible that odd columns be staggered relative to even columns. Other variations are also possible, and within the scope of an embodiment of the present invention. In the embodiment shown in FIG. 2A, the Tx MUTs 223 and the Rx MUTs 225 alternate in a way that creates minimum pitch in linear array configuration, thereby enabling better lateral resolution.

As will be described in further detail below, at any given time, a set of the Tx MUTs 223 can be selected for transmitting ultrasonic pulses, and a set of the Rx MUTs 225 can be selected for receiving echo pulses. For example, sets of Tx MUTs 223 that collectively make up rings can be used to form a quasi-annular array transducer, as will be described below with reference to FIGS. 3-5. Switches 222, which can be referred to as Tx switches 222, can be used to select which Tx MUTs 223 are active at a time. Similarly, switches 216, which can be referred to as Rx switches, can be used to select which Rx MUTs 225 are active at a time. In accordance with an embodiment, each of the Tx MUTs 223 is connected to a corresponding Tx switch. When the Tx switch is turned on (which can also be referred to as closed), the Tx MUT 223 is connected by its corresponding Tx switch to the HV pulser 224, thereby causing the Tx MUT 223 to output an ultrasonic pulse. When multiple MUTs 223 are triggered simultaneously (i.e., simultaneously connected by switches to the HV pulser 224), the multiple MUTs collectively produce an ultrasonic pulse or wave-front.

Selected Tx MUTs 223 transmit ultrasonic pulses into the target region being examined, and selected Rx MUTs 225 receive reflected ultrasonic pulses (i.e., “echo pulses”) returning from the region. When transmitting, the selected Tx MUTs 223 are excited to high-frequency oscillation by the pulses emitted by the HV pulser 224, thereby generating ultrasound pulses that can be directed at a target region/object to be imaged.

These ultrasound pulses (also referred to as ultrasonic pulses) produced by the selected Tx MUTs 223 are echoed back towards the selected Rx MUTs 225 from some point within the target region/object, e.g., at boundary layers between two media with differing acoustic impedances. The echo pulses received by the selected Rx MUTs 225 are converted into corresponding low-level electrical input signals (i.e., the “echo signals”) that are provided to the analog summing, amplification and processing circuitry 215. In specific embodiments, to receive echo pulses, the Rx switches 216 selectively connect a set of the Rx MUTs 225 to summing resistors 214, which are used to sum the echo pulses at the input of a summing amplifier 212.

Advantageously, in certain embodiments, the vectors may be uploaded to memory (look-up-table) 230 from Host Computer 112 in order to upgrade probe 102 or provide a set of vectors suitable for a particular imaging application. For example different vectors can be provided for imaging different portions of the human body, different tissues, or different depths depending on the application. A user can select the appropriate application (imaging purpose) in the host computer 112 which can then transfer an appropriate vector set to memory 230 over passive interface cable 106 prior to imaging. Alternatively memory 230 can include a plurality of vector sets suitable for different applications and the user can select which of those vector sets is used by Tx/Rx Controller 215 in a particular imaging session by input to host computer 112 or using an interface/switch/multiposition switch on probe housing 103. After download or selection of a pre-existing vector set in memory 230, the vector set can be used by Tx/Rx Controller 215 to configure Tx switches 222 and Rx switches 216 to cause Tx MUTS 223 and Rx MUTS 225 to transmit and receive ultrasound pulses in accordance with the downloaded vectors suitable for the intended application.

FIG. 2B illustrates some further details of some of the blocks introduced in FIG. 2A, according to an embodiment of the present invention. In specific embodiments, to receive echo pulses, the Rx switches 216 selectively connect a set of the Rx MUTs 225 to summing resistors 214, which are used to sum the echo pulses at the input of a summing amplifier 212. In accordance with an embodiment, the analog summing, amplification and processing circuitry 215 includes summing resistors 214 and a summing amplifier 212. Exemplary details of the Rx switches 216, the summing resistors 214 and the summing amplifier 212 are shown in FIG. 2B.

Note that, as previously discussed, single channel architecture is used. Accordingly, the Rx switches 216 (or Tx/Rx) switches connect a plurality of selected MUTS 225 to analog summing, amplification and signal processing circuitry 215. Note that there are a plurality of summing resistors 214 in order that they may be connected to a selected plurality of Rx MUTS 225. Analog summing, amplification and signal processing circuitry 215 is configured to combine the plurality of echo signals produced by the plurality of the ultrasound transducers 225 into a single analog echo signal. This can be achieved using summing amplifier 212. A single analog-to-digital converter 208 (ADC) then converts the analog echo signal into a single digital echo signal for transmission to a host computer that can perform digital processing of the digital echo signal in order to display an ultrasound image.

FIG. 2C illustrates a perspective view of a probe head assembly, according to an embodiment of the present invention. A shown in FIG. 2C, MUT array 220 is positioned at the end of head assembly 105. FIG. 2C also shows a portion of the interface cable 209, which is used to connect the components within the probe head assembly 105 to components within the probe housing 103.

FIG. 2D illustrates how odd and even rows of MUTS 221 can be staggered relative to one another. All of the rows and columns can be inline with one another, as shown in FIG. 2A. Alternatively, odd rows can be staggered relative even rows, as shown in FIG. 2D. It is also possible that odd columns be staggered relative to even columns. Other variations are also possible, and within the scope of an embodiment of the present invention. In the embodiment shown in FIG. 2D, the Tx MUTs 223 and the Rx MUTs 225 alternate in a way that creates minimum pitch in linear array configuration, thereby enabling better lateral resolution. As mentioned above, sets of Tx MUTs 223 that collectively makes up rings/circles that can be used to form a quasi-annular array transducer, as described below with reference to FIGS. 3A-5D.

FIG. 2E illustrates an alternative array of ultrasound transducers according to an embodiment of the present invention. As shown in FIG. 2E, an alternative ultrasound transducer array 260 includes a regular distribution of 128 rectangular ultrasound transducers 262 arranged in a linear array (single row). In alternative embodiments transducer array 260 may be square, rectangular, linear or another shape and may comprise one, or a plurality of, rows and/or columns of transducers. Transducer array 260 may comprise a different number of transducers depending on the application. For example, transducer array 260 may comprise 8, 16, 32, 64, 128, 256 or more transducers 262. Transducers 262 may be any suitable shape for assembly into an array including for example, square, rectangular, or circular. Alternative transducer array 260 may be used in place of MUT array 220 in all embodiments described herein.

Transducer array 260 is preferably planar in shape i.e. all of transducers 262 lay in a single flat plane (not curved). Moreover, in preferred embodiments no lens or other beam forming device is placed over transducer array 260. Accordingly, similar or identical ultrasound beams can be produced by similar groups of transducers 262 at different locations in transducer array 260.

Transducers 262 can be made using conventional technology known in the art and may be, for example, piezo-electric transducers or capacitive transducers. In an embodiment ultrasound transducers 262 are substantially rectangular piezoelectric transducers approximately 5 mm by 0.3 mm in size. A set of 16 adjacent transducers acting together form a substantially square ultrasound source.

As shown in FIG. 2F, Transducers 262 are selectively connected by Tx/Rx switches 266 to HV pulser 224 and analog processing circuitry 215. Each of ultrasound transducers 262 may be used for transmitting ultrasound pulses or receiving ultrasound echoes depending on the configuration of the Tx/Rx switches 266 as controlled by Tx/Rx Controller 240. Alternatively, certain transducers 262 may be used only for transmitting ultrasound pulses and other may be used only for detecting ultrasound echoes. In this alternative embodiment, switches Tx switches 222 and Rx switches 216 are used in place of Tx/Rx switches 266.

Note that, as previously discussed, single channel architecture is used in combination with transducer array 260. Accordingly, the Tx/Rx switches 266 (or Rx switches 216 in an alternative embodiment) connect the plurality of selected transducers 262 to analog summing, amplification and signal processing circuitry 215 which is configured to combine echo signals produced by a plurality of the ultrasound transducers 262 into a single analog echo signal. A single analog-to-digital converter (ADC) then converts the analog echo signal into a digital echo signal for transmission to a host computer that can perform digital processing of the digital echo signal in order to display an ultrasound image.

FIG. 2F is a block diagram that shows details of an alternative ultrasonic imaging probe according to an embodiment of the present invention. FIG. 2F has almost all the elements of FIG. 2A as previously described. However MUT Array 220 has been replaced transducer array 260. Additionally, Tx/Rx switches 266 are used in place of the Tx switches 222 and Rx switches 216 of FIG. 2A such that each of the ultrasound transducers 262 may be used for transmitting or receiving ultrasound depending on the configuration of the Tx/Rx switches 266 at a particular point in time.

The Tx/Rx switches 266 can be used to connect a selected set of the transducers 262 to either the HV pulser 224, or the analog summing, amplification and processing circuitry 215, depending on whether the transducers 262 are to be used for transmitting or receiving ultrasound pulses at a particular time. When a high voltage pulse is produced by the HV pulser 224, the Tx/Rx switches automatically block the high voltage from damaging the analog summing, amplification and processing circuitry 215. When the HV pulser 224 is not producing a pulse, the Tx/Rx switches disconnect a selected set of transducers 262 from the pulser 224, and instead connect a selected set of transducers 262 to the analog summing, amplification and processing circuitry 215. Note that Tx/Rx switches 266 may also be used in combination with MUT array 220 (see, e.g. FIGS. 2A and 2D).

FIG. 3A illustrates how sets of micromachined ultrasound transducers (MUTs) that collectively make up rings can be used to form a quasi-annular array transducer, and that such rings can be moved to emulate the mechanical movement of an annular array transducer, without requiring any moving parts. Referring to FIG. 3A, illustrated therein are a plurality of possible MUT vectors, each of which is made up of a plurality of annular rings/circles of MUTs 221. Each such vector can be made up of a plurality of different sets of MUTs 221, wherein each set of MUTs defines a different annular ring/circle of MUTs 221, as can be appreciated from the discussion of FIGS. 4A-4D below. Still referring to FIG. 3A, illustrated therein are four different MUT vectors, the first one of which is labeled Vector 1, and the last one of which is labeled Vector X. If, e.g., X=128, that would mean that 128 of the annular array MUT vectors can be produced using the MUT array 220. More specifically, by controlling the Tx and Rx switches 222 and 216 (in FIG. 2A), the various MUT Vectors (1 through 128) can be selected, one after the other, to emulate an annular array (annular shaped ultrasound transmitter) that is mechanically moved through 128 different physical positions (as shown by arrow 300). However, here there is no mechanical movement; but rather, different MUTs 221 are selected at sequential points in time in order to emulate the movement. Thus, by controlling the Tx switches 222 to select different groups of Tx MUTS 223 at different times, the transmitting group of transducers forms an ultrasound transmitter which effectively changes position within the array of transducers over time. Similarly by controlling the Rx switches 216 to select different groups of Rx MUTS 225 at different times, the receiving group of transducers forms an ultrasound receiver which effectively changes position within the array of transducers over time.

FIG. 3B is a blown-up view of two of the closely spaced adjacent vectors, X/2 and X/2+1, shown in FIG. 3A. FIG. 3B shows a MUT array 220 which includes a plurality of MUTs 221, some or all of which may function as Tx MUTs 223 and some or all of which may function a Rx MUTs 225. The adjacent vectors X/2 and X/2+1 show how different groups of Tx MUTS 223 and Rx MUTS 225 are selected (by Tx switches 222 and Rx switches 216 configured by Tx/Rx controller 240) for transmitting and receiving ultrasound pulses at different sequential periods in time. As, shown, in the embodiments shown in FIGS. 3A and 3B, the Tx MUTs 223 and the Rx MUTs 225 alternate in a way that creates minimum pitch in linear array configuration, thereby enabling better lateral resolution.

FIGS. 3C-3F show how sets of ultrasound transducers 262 of ultrasound transducer array 260 of FIGS. 2E and 2F can be used to form a moving square array transducer according to an embodiment of the present invention. In each of FIGS. 3C-3F the set 350, 360, 370, 380 of transducers 262 connected by Tx/Rx switches to HV pulser 224 as indicated by shading of transducers 262. Each set 350, 360, 370, 380 of sixteen adjacent transducers operates as a single square ultrasound transmitter. Alternative shapes of transmitter may be configured from different sets of transducers 262. As shown by FIGS. 3C-3F the active set of transducers can be moved without mechanical movement merely by selecting different transducers 262 for inclusion in the active set at a particular time. Thus the portion or subarray of transducer array 260 that is emitting ultrasound can “walk” around transducer array 260 under the control of Tx/Rx switches 266 as configured by Tx/Rx Controller 240. Likewise the size, shape, and/or position of the set of transducers 262 connected to analog processing circuitry 215 can also be changed from one period of time to the next.

FIGS. 4A-4D illustrate how a transmit MUT vector can be used to transmit focused ultrasound beams. FIGS. 4A-4D illustrates different sized groups of Tx MUTs 223 rings/circle of Tx MUTs 223, which can collectively be used to generate one focused ultrasound beam. The different groups of Tx MUTS 223 and Rx MUTS 225 are selected (by Tx switches 222 and Rx switches 216 configured by Tx/Rx controller 240) for transmitting and receiving ultrasound pulses at different sequential periods in time. More specifically, the ring 410 of Tx MUTs 223 shown in FIG. 4A can be used to collectively transmit a first ultrasound pulse. A short programmed delay thereafter the ring 420 of Tx MUTs 223 shown in FIG. 4B can be used to collectively transmit a second ultrasound pulse. A short programmed delay thereafter the ring 430 of Tx MUTs 223 shown in FIG. 4C can be used to collectively transmit a third ultrasound pulse. And, a short programmed delay thereafter the circle 440 of Tx MUTs 223 shown in FIG. 4D can be used to collectively transmit a fourth ultrasound pulse. These four ultrasound pulses, sequentially generated as mentioned above, collectively make up a focused ultrasound beam.

By controlling the Tx switches 222 to select different groups of Tx MUTS 223 at different times, the transmitting group of transducers forms an ultrasound transmitter which effectively changes shape and/or size and/or position over time. As shown in FIGS. 4A-4D, the ring 410 in FIG. 4A has the largest aperture, and the circle 440 in FIG. 4D has the smallest/no aperture. In FIGS. 4A-4D, the four different rings/circle 410, 420, 430, 440, do not overlap one another. However, in alternative embodiments, there can be overlap between the different rings/circle. In other words, a Tx MUT 223 can be included in more than one annular ring/circle.

FIGS. 5A-5D illustrate how a receive MUT vector can be used to receive echo pulses generated in response to the focused ultrasound beam described with reference to FIGS. 4A-4D. FIGS. 5A-5D illustrates different sized circles of Rx MUTs 225, which can collectively be used to receive echo pulses and produce an echo signal. More specifically, the circle 510 of Rx MUTs 225 shown in FIG. 5A can be used to collectively receive a first echo pulse; a short programmed delay thereafter the circle 520 of Rx MUTs 225 shown in FIG. 5B can be used to collectively receive a second echo pulse; a short programmed delay thereafter the circle 530 of Rx MUTs 225 shown in FIG. 5C can be used to collectively receive a third echo pulse; and a short programmed delay thereafter the circle 540 of Rx MUTs 225 shown in FIG. 5D can be used to collectively receive a fourth echo pulse. These four echo pulses collectively make up a received ultrasound echo.

By controlling the Rx switches 216 to select different groups of Rx MUTS 225 at different times, the receiving group of transducers forms an ultrasound receiver which effectively changes shape, size, or position within the array of transducers over time. As shown in FIGS. 5A-5D, the circle 510 of Rx MUTs 225 in FIG. 5A, which has the smallest diameter, will receive near field echoes. By contrast, the circle 540 of Rx MUTs 225 in FIG. 5D, which has the largest diameter, will receive the deepest field echoes. In FIGS. 5A-5D, the four different circles 510, 520, 530, 540, overlap one another. However, in alternative embodiments, there can be no overlap between the different circles. In other words, an Rx MUT 225 may or may not be included in more than one circle. Further, it is noted that sets of the Rx MUTs 225 can be selected in such a way that the active area of circular arrays can continuously increase with a controlled number of sampling cycles in order to optimize the resolution of the received signal from different depths.

Tx/Rx Controller 240 controls Tx switches 222 and Rx switches 216 to select different groups of Tx MUTs 223 and Rx MUTS 225 at different times for sending and receiving ultrasound transducers thereby allowing the MUT Array 220 to emulate an ultrasound receiver and ultrasound transmitter which effectively changes in shape, size, or position within the array of transducers over time. While the Tx MUT and Rx MUT vectors shown in FIGS. 4A-4D and 5A-5D include substantially circular and/or annular arrays, because of the flexibility provided by the MUT array 220, the vectors can have alternative shapes, such as, but not limited to elliptical shapes. In alternative embodiments, the Tx MUTs 223 and Rx MUTs 225 can be selectively connected to produce other types of arrays, besides circular and/or annular arrays. In embodiments, the vectors are stored in memory (look-up-table) 230.

Advantageously, the MUT array 220 and the circuitry used to select sets of the MUTs can provide a continuously variable aperture annular array. More specifically, such circuitry can be used to activate sets of MUTs in such a way that the active area of annular arrays will continuously shift in order to form ultrasound beams with variable focal points. In other words, the MUT array 220 can be used to perform beam forming and aperture control for each of a plurality of different MUT vectors. Advantageously, beam shapes and aperture shapes and sizes can be optimized for both transmit and receive signals.

In accordance with certain embodiments of the present invention, preprogrammed vector configuration and timing data that enables the various annular rings of Tx MUTs 223 shown in FIGS. 4A-4D to be fired in sequence is stored in the memory 230, e.g., in a LUT. Similar data used to controls selection/activation of Rx MUTs, as was described with reference to FIGS. 5A-5D, is also stored in the memory 230 (see FIG. 2A).

FIGS. 6A-6D illustrate how a vectors can be used to receive echo pulses generated in response to an ultrasound beam using transducer array 260 of FIGS. 2E and 2F. FIGS. 6A-6D illustrates different sized groups/subarrays 660, 670, 680, 690 of ultrasound transducers 262 (shaded), which can collectively be used to receive echo pulses and produce an echo signal. More specifically, the subarray 660 of ultrasound transducers 262 shown in FIG. 6A can be used to collectively receive a first echo pulse; a short programmed delay thereafter the subarray 670 of ultrasound transducers 262 shown in FIG. 6B can be used to collectively receive a second echo pulse; a short programmed delay thereafter the subarray 680 of ultrasound transducers 262 shown in FIG. 6C can be used to collectively receive a third echo pulse; and a short programmed delay thereafter the subarray 690 of ultrasound transducers 262 shown in FIG. 6D can be used to collectively receive a fourth echo pulse. These four echo pulses collectively make up a received ultrasound echo.

By controlling the Tx/Rx switches 266 to select different groups of ultrasound transducers 262 (shaded) at different times, the receiving group of transducers forms an ultrasound receiver which effectively changes shape, size, or position within the array of transducers 260 over time. As shown in FIGS. 6A-6D, the subarray 660 of ultrasound transducers 262 shown in FIG. 6A, which has the smallest size, will receive near field echoes. By contrast, the subarray 690 of ultrasound transducers 262 shown in FIG. 6 dD which has the largest size will receive the deepest field echoes. The increasing subarray size effectively provides a variable aperture for receiving ultrasound echoes in order to enhance the resolution of the received signal from different depths. The variable aperture for receiving may be utilized with fixed or variable sizes of transmitting subarrays of ultrasound transducers.

In FIGS. 6A-6D, the four different subarrays 660, 670, 680, 690, overlap one another. However, in alternative embodiments, there can be no overlap between the different subarrays. In other words, a transducer 262 may or may not be included in more than one subarray. Further, it is noted that subarrays of the transducers 262 can be selected in such a way that the active area of the subarray can continuously increase with a controlled number of sampling cycles in order to optimize the resolution of the received signal from different depths.

Tx/Rx Controller 240 controls Tx/Rx switches 266 (see FIG. 2F) to select different groups of transducers 262 at different times for sending and receiving ultrasound transducers thereby allowing the ultrasound array 260 to emulate an ultrasound receiver and ultrasound transmitter which effectively changes in shape, size, or position within the array of transducers over time. Because of the flexibility provided by the transducer array 260, the vectors can have alternative shapes. In embodiments, the vectors are stored in memory (look-up-table) 230. Subarrays may comprise non-adjacent transducers 262, i.e. within a region of transducer array 260 certain transducers may be active for receiving (or transmitting) ultrasound while other are inactive depending on the desired vectors.

As described above with respect to the figures, in an embodiment, the present invention provides a portable ultrasonic imaging probe 102 that is adapted to connect to a host computer 112 via a passive interface cable 106. The portable ultrasound imaging probe 106 includes a probe head 105 including an array of ultrasound transducers, for example MUT Array 220. The array may comprise one or more parallel rows of ultrasound transducers, or a different shaped distribution of a plurality of ultrasound transducers. The ultrasound transducers may be, for example, micromachined ultrasound transducers MUTS 221 or other ultrasound transducers known in the art.

The portable ultrasonic imaging probe 102 also includes a pulse circuit, for example, a high voltage (HV) pulser 224 adapted to energize two or more transducers to emit ultrasound. The portable ultrasonic imaging probe 102 also includes analog processing circuitry 215, including for example summing amplifier 212, and summing resistors 214, configured to process electrical signals caused by ultrasound pulses received by two or more ultrasound transducers into an analog echo signal. One or more analog-to-digital converters (e.g. ADC 208) converts the analog echo signal, output by the analog summing, amplification and signal processing circuitry, to a digital echo signal, and an interface circuit 204 transfers the digital echo signal across a passive interface cable to a host computer that can perform digital processing of the digital echo signal in order to display an ultrasound image.

The portable ultrasonic imaging probe 102 also includes a transmit/receive controller 215 connected to a plurality of transmit (Tx) switches 222 and a plurality of receive (Rx) switches 216 wherein the transmit/receive controller 215 selects which of said ultrasound transducers are in transmitting group and which of said ultrasound transducers are in the receiving group at any point in time. The transmit/receive controller 215 configures the plurality of transmit (Tx) switches 222 to connect a transmitting group of the ultrasound transducers to the (HV) pulser 224. The transmit/receive controller 215 also configures a plurality of receive (Rx) switches 2′6 to connect a receiving group of the ultrasound transducers to the analog summing, amplification and signal processing circuitry 215.

The portable ultrasonic imaging probe 102 operates such that which ultrasound transducers of the ultrasound transducer array are part of the receiving group and which are part of the receiving group is configurable and can be changed over time under the control of transmit/receive controller 215 in response. Transmit and receive (Tx/Rx) controller 240 accesses vector configuration and timing data stored within a memory 230 to identify which transducers should be activated for transmitting (transmitting group) or receiving ultrasound pulses (receiving group) and at what time.

In accordance with the vector configuration and timing data the transmitting group includes a first plurality of transducers at a first time, a second plurality of transducers different than the first plurality at a second time, and a third plurality of transducers different than the first plurality and the second plurality a third time. The configurable transmitting group functions as a configurable ultrasound transmitter which can change in shape, size or position within the transducer array over time. This allows, for example the ultrasound imaging probe 102 to: emit a focused ultrasound beam; change the depth or focus or position of focus of the ultrasound beam; perform ultrasound beam forming; scan the ultrasound beam without moving the head 105; and/or form a variable aperture ultrasound transmitter; and use configurable aperture control.

In accordance with the vector configuration and timing data the receiving group includes a first plurality of transducers at a first time, a second plurality of transducers different than the first plurality at a second time, and a third plurality of transducers different than the first plurality and the second plurality a third time. The configurable receiving group functions as a configurable ultrasound receiver which can change in shape, size or position within the transducer array over time. This allows, for example the ultrasound imaging probe 102 to: change the size, shape, or position of the configurable ultrasound receiver over time (in relation, for example, to the timing of the emission of ultrasound pulses). The receiving group can be selected in such a way that the active area of receiving transducers can be configured and changed over a number of sampling cycles in order to optimize the resolution of the received signal from different depths, different tissues, and in different applications.

In alternative embodiments, rather than having half the MUTs 221 dedicated to functioning as Tx MUTs 223, and half the MUTs 221 dedicating to functioning as Rx MUTs 225, each of the MUTs 221 of the MUT array 220 can be capable of being used as either an Rx MUT 223 or a Tx MUT 225. In such alternative embodiments, transmit/receive (Tx/Rx) switches (not shown) can be used in place of the Tx switches 222 and the Rx switches 216. The Tx/Rx switches can be used to connect a selected set of the MUTs 221 to either the HV pulser 224 or the analog summing, amplification and processing circuitry 215 depending on whether the MUTs 221 are to be used for transmitting or receiving ultrasound pulses at a particular time. When a high voltage pulse is produced by the HV pulser 224, the Tx/Rx switches would automatically block the high voltage from damaging the analog summing, amplification and processing circuitry 215. When the HV pulser 224 is not producing a pulse, the Tx/Rx switches disconnect a selected set of MUTs 221 from the HV pulser 224, and instead connect a selected set of MUTs to the analog summing, amplification and processing circuitry 215. However, Tx/Rx switches are relatively expensive compared to switches required to perform only one of the Tx switching and Rx switching functions. Accordingly, the aforementioned embodiments where certain MUTs 221 are dedicated to transmission, and other MUTs 221 are dedicated to reception, such a configuration may be preferable where it is desirable to eliminate the need for expensive Tx/Rx switches.

The foregoing description of preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to one of ordinary skill in the relevant arts. The above mentioned part numbers are exemplary, and are not meant to be limiting. Accordingly, other parts can be substituted for those mentioned above.

The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents. 

What is claimed is:
 1. A portable ultrasonic imaging probe that is adapted to connect to a host computer via a passive interface cable, the portable ultrasound imaging probe comprising: a probe head including an array of ultrasound transducers; a high voltage (HV) pulser adapted to energize two or more transducers to emit ultrasound; analog summing, amplification and signal processing circuitry configured to combine echoes detected by two or more ultrasound transducers into a single analog echo signal; a single analog-to-digital converter (ADC) that converts the analog echo signal, output by the analog summing, amplification and signal processing circuitry, to a digital echo signal; and interface circuitry adapted to transfer the digital echo signal across a passive interface cable to a host computer that can perform digital processing of the digital echo signal in order to display an ultrasound image; a plurality of transmit (Tx) switches configured to connect a transmitting group of the ultrasound transducers to the (HV) pulser; a plurality of receive (Rx) switches configured to connect a receiving group of the ultrasound transducers to the analog summing, amplification and signal processing circuitry; a transmit/receive controller connected to the plurality of transmit (Tx) switches and the plurality of receive (Rx) switches wherein the transmit/receive controller selects which of said ultrasound transducers are in the transmitting group and which of said ultrasound transducers are in the receiving group.
 2. The portable ultrasonic imaging probe of claim 1, wherein said transmitting group of ultrasound transducers comprises: a first plurality of transducers at a first time; a second plurality of transducers different than the first plurality at a second time; and a third plurality of transducers different than the first plurality and the second plurality a third time; whereby the ultrasound imaging probe emits a focused ultrasound beam.
 3. The portable ultrasonic imaging probe of claim 1, wherein said transmitting group of ultrasound transducers comprises: a first plurality of transducers at a first time; a second plurality of transducers different than the first plurality at a second time; and a third plurality of transducers different than the first plurality and the second plurality a third time; whereby the transmitting group of transducers forms an ultrasound transmitter which changes in position within the array of transducers between the first time, the second time and the third time.
 4. The portable ultrasonic imaging probe of claim 1, wherein said transmitting group of ultrasound transducers comprises: a first plurality of transducers at a first time, wherein the first plurality of transducers form a first annular cluster in said array of transducers; a second plurality of transducers different than the first plurality at a second time, wherein the second plurality of transducers form a second annular cluster in said array of transducers; and a third plurality of transducers different than the first plurality and the second plurality a third time, wherein the third plurality of transducers form a third annular cluster in said array of transducers; wherein the first annular cluster has a larger aperture diameter than the second annular cluster, and the second annular cluster has a larger aperture than the third annular cluster such that the transmitting group of transducers forms a variable aperture ultrasound transmitter.
 5. The portable ultrasonic imaging probe of claim 1, wherein said receiving group of ultrasound transducers comprises: a first plurality of transducers at a first time; a second plurality of transducers different than the first plurality at a second time; and a third plurality of transducers different than the first plurality and the second plurality a third time; whereby the receiving group of transducers forms an ultrasound receiver which changes in size between the first time, the second time and the third time.
 6. The portable ultrasonic imaging probe of claim 1, wherein said receiving group of ultrasound transducers comprises: a first plurality of transducers at a first time; a second plurality of transducers different than the first plurality at a second time; and a third plurality of transducers different than the first plurality and the second plurality a third time; whereby the receiving group of transducers forms an ultrasound receiver which changes in position between the first time, the second time and the third time.
 7. The portable ultrasonic imaging probe of claim 1, wherein: said transmitting group of ultrasound transducers comprises a first plurality of transducers at a first time, a second plurality of transducers different than the first plurality at a second time, and a third plurality of transducers different than the first plurality and the second plurality a third time; and said receiving group of ultrasound transducers comprises a fourth plurality of transducers at a fourth time; a fifth plurality of transducers different than the fourth plurality at a fourth time; and a sixth plurality of transducers different than the fourth plurality and the fifth plurality at a sixth time.
 8. The portable ultrasonic imaging probe of claim 1, wherein said array of transducers comprises a plurality of ultrasound transducers arranged in a row.
 9. The portable ultrasonic imaging probe of claim 1, wherein said array of transducers comprises a plurality of ultrasound transducers arranged in plurality of parallel rows.
 10. The portable ultrasonic imaging probe of claim 1, wherein said transducers are micromachined ultrasound transducers (MUTs).
 11. A portable ultrasonic imaging probe that is adapted to connect via a passive interface cable to a host computer that can perform digital processing in order to display an ultrasound image, the portable ultrasound imaging probe comprising: a probe head including an array of ultrasound transducers; a power circuit adapted to energize two or more transducers to emit ultrasound; analog processing circuitry configured to combine echoes detected by two or more ultrasound transducers into an analog echo signal; an analog-to-digital converter (ADC) that converts the analog echo signal, output by the analog signal processing circuitry, into a single channel digital echo signal; and interface circuitry adapted to transfer the digital echo signal across a passive interface cable to the host computer for digital processing in order to display an ultrasound image; a plurality of switches configured to connect a transmitting group of the ultrasound transducers to the power circuit and configured to connect a receiving group of the ultrasound transducers to the analog processing circuitry; a transmit/receive controller connected to the plurality of switches, wherein the transmit/receive controller selects which of said ultrasound transducers are in the transmitting group and which of said ultrasound transducers are in the receiving group.
 12. The portable ultrasonic imaging probe of claim 11, wherein said transmitting group of ultrasound transducers comprises: a first plurality of transducers at a first time; a second plurality of transducers different than the first plurality at a second time; and a third plurality of transducers different than the first plurality and the second plurality a third time; whereby the ultrasound imaging probe emits a focused ultrasound beam.
 13. The portable ultrasonic imaging probe of claim 11, wherein said transmitting group of ultrasound transducers comprises: a first plurality of transducers at a first time; a second plurality of transducers different than the first plurality at a second time; and a third plurality of transducers different than the first plurality and the second plurality a third time; whereby the transmitting group of transducers forms an ultrasound transmitter which changes in position within the array of transducers between the first time, the second time and the third time.
 14. The portable ultrasonic imaging probe of claim 11, wherein said transmitting group of ultrasound transducers comprises: a first plurality of transducers at a first time, wherein the first plurality of transducers form a first annular cluster in said array of transducers; a second plurality of transducers different than the first plurality at a second time, wherein the second plurality of transducers form a second annular cluster in said array of transducers; and a third plurality of transducers different than the first plurality and the second plurality a third time, wherein the third plurality of transducers form a third annular cluster in said array of transducers; wherein the first annular cluster has a larger aperture diameter than the second annular cluster, and the second annular cluster has a larger aperture than the third annular cluster such that the transmitting group of transducers forms a variable aperture ultrasound transmitter.
 15. The portable ultrasonic imaging probe of claim 11, wherein said receiving group of ultrasound transducers comprises: a first plurality of transducers at a first time; a second plurality of transducers different than the first plurality at a second time; and a third plurality of transducers different than the first plurality and the second plurality a third time; whereby the receiving group of transducers forms an ultrasound receiver which changes in size between the first time, the second time and the third time.
 16. The portable ultrasonic imaging probe of claim 11, wherein said receiving group of ultrasound transducers comprises: a first plurality of transducers at a first time; a second plurality of transducers different than the first plurality at a second time; and a third plurality of transducers different than the first plurality and the second plurality a third time; whereby the receiving group of transducers forms an ultrasound receiver which changes in position between the first time, the second time and the third time.
 17. The portable ultrasonic imaging probe of claim 11, wherein: said transmitting group of ultrasound transducers comprises a first plurality of transducers at a first time, a second plurality of transducers different than the first plurality at a second time, and a third plurality of transducers different than the first plurality and the second plurality a third time; and said receiving group of ultrasound transducers comprises a fourth plurality of transducers at a fourth time; a fifth plurality of transducers different than the fourth plurality at a fourth time; and a sixth plurality of transducers different than the fourth plurality and the fifth plurality at a sixth time.
 18. The portable ultrasonic imaging probe of claim 11, wherein said array of transducers comprises a plurality of ultrasound transducers arranged in a row.
 19. The portable ultrasonic imaging probe of claim 1, wherein said array of transducers comprises a plurality of ultrasound transducers arranged in plurality of parallel rows.
 20. The portable ultrasonic imaging probe of claim 1, wherein said transducers are micromachined ultrasound transducers (MUTs).
 21. A portable ultrasonic imaging probe that is adapted to connect via a USB cable to a host computer that can perform digital processing in order to display an ultrasound image, the portable ultrasound imaging probe comprising: a probe head including an array of ultrasound transducers; a power circuit adapted to energize two or more transducers to emit ultrasound; analog processing circuitry configured to combine echoes detected by two or more ultrasound transducers into an analog echo signal; an analog-to-digital converter (ADC) that converts the analog echo signal, output by the analog signal processing circuitry, into a single digital echo signal; and interface circuitry adapted to transfer the digital echo signal across said USB cable to the host computer for digital processing in order to display an ultrasound image; a plurality of switches configured to connect a transmitting group of the ultrasound transducers to the power circuit and configured to connect a receiving group of the ultrasound transducers to the analog processing circuitry; wherein said transmitting group of ultrasound transducers comprises: a first plurality of transducers at a first time, a second plurality of transducers different than the first plurality at a second time, and a third plurality of transducers different than the first plurality and the second plurality a third time.
 22. The portable ultrasonic imaging probe of claim 21 wherein said transmitting group of transducers forms an ultrasound transmitter which changes in position within the array of transducers between the first time, the second time and the third time.
 23. The portable ultrasonic imaging probe of claim 21, wherein: the first plurality of transducers forms a first annular cluster in said array of transducers; the second plurality of transducers form a second annular cluster in said array of transducers; and the third plurality of transducers forms a third annular cluster in said array of transducers; wherein the first annular cluster has a larger aperture diameter than the second annular cluster, and the second annular cluster has a larger aperture than the third annular cluster such that the transmitting group of transducers forms a variable aperture ultrasound transmitter.
 24. The portable ultrasonic imaging probe of claim 21, wherein said receiving group of ultrasound transducers comprises: a fourth plurality of transducers at a fourth time; a fifth plurality of transducers different than the fourth plurality at a fifth time; and a sixth plurality of transducers different than the fourth plurality and the fifth plurality at a sixth time; whereby the receiving group of transducers forms an ultrasound receiver which changes in size between the fourth time, the fifth time and the sixth time.
 26. The portable ultrasonic imaging probe of claim 21, wherein said receiving group of ultrasound transducers comprises: a fourth plurality of transducers at a fourth time; a fifth plurality of transducers different than the fourth plurality at a fifth time; and a sixth plurality of transducers, different than the fourth plurality and the fifth plurality, at a sixth time; whereby the receiving group of transducers forms an ultrasound receiver which changes in position between the fourth time, the fifth time and the sixth time.
 27. The portable ultrasonic imaging probe of claim 21, wherein said array of transducers comprises a plurality of ultrasound transducers arranged in a row.
 28. The portable ultrasonic imaging probe of claim 21, wherein said array of transducers comprises a plurality of ultrasound transducers arranged in plurality of parallel rows.
 29. The portable ultrasonic imaging probe of claim 21, wherein said transducers are micromachined ultrasound transducers (MUTs).
 30. The portable ultrasonic imaging probe of claim 21, in combination with said host computer and a USB cable connecting said interface circuitry to said host computer. 